Spaulding succeeds Katrina Lake, the founder and current CEO, who becomes executive chairwoman.
In her previous role as president, Spaulding had focused on what the company called expanding "the next generation of consumer shopping experiences"; innovating in Inventory management, and broadening the company's efforts overseas.
Before joining Stitch Fix, Spaulding had spent more than 20 years at the management consultant Bain & Co., where she was a partner, a member of the board, and founder and global head of the digital practice.
As chairwoman, Lake will particularly focus on the company's social impact efforts, particularly the connection between sustainability and technology in apparel retail, the company said.
Lake founded Stitch Fix in 2011 as a Harvard Business School student. The company went public in 2017. It now posts annual revenue of $1.70 billion and employs 8,000 people.
In her role at Stitch Fix, reporting to Spaulding, Chiarella will lead the product and experience group, which includes the product, design and technical teams that help drive the company's business model.
Stitch Fix's stylists and algorithms recommend personalized selections of apparel, shoes and accessories to individual customers.
During 13 years at Amazon Chiarella spearheaded customer-experience features including customer videos and Q&A and one-tap star ratings.
At last check Stitch Fix shares were off 4.4% at $47.30. They finished the regular Tuesday trading session down 2.5% at $49.49.